Automatic volume control



Slept. 22, 1936.

AR. A. BRADEN AUTOMATIC VOLUME CONTROL Filed June 26, 1933 N M RE Y OD ETA N NRR @D m A me A Patented Sept. 22, 1936 UNITED STATES i 2,055,314AUToMATlo voLUME CONTROL Rene A. Braden, Collingswood, N. J.; assignorto Radio Corporation of America, a corporation of Delaware l ApplicationJune 26, 1933, serial No.` 67%,614

7 Claims;

. My present invention relates to high frequency amplifier gain controlcircuits, and more particularly to an arrangementfor automaticallyregulating the gain-of radio frequency amplifier circuits.

In allautomatic gain control arrangements for the high frequencyamplifier circuits of radio receivers there exists an ideal automaticvolume control action which is sought to be attained. Briefly, it may bestated that this idealis to increase the stiffness Vof the automaticvolume control action as economically as possible; Various devices andarrangements have been utilized to approach this ideal operation.

It may be stated that it is one of the main objects of my presentinvention to provide an automatic Volume control arrangement for a radioreceiver wherein the stiffness of automatic volume control is secured atsubstantially negligible expense by employing, vin conjunction with theusual automatic volume control tube, an elementcapable of maintainingthe voltagef drop across it substantially Aconstant with increasing flow`of current through-this element.

Another important object of the present invention is to provide in anautomatic volume control network for a highfrequency amplifier aneconomical fcrm of voltage regulator, the latter convsisting of acarborundum material, and being ca- ..trolled,'a.voltag`e regulatorelement composed subv stantiallyof carborundum, the voltage regulatorelement being connected in the anode circuit of vthe volume controlrectifier. i

pable of having the voltage drop across itself 'substantially constantover a wide range of current variation.

Still anotherobject of the present invention is to provide incombination with anjautor'natic volume control arrangement .adapted tocontrol the potential ofla highfrequency amplifier control grid, orscreen grid, and which automatic Volume controllarrangement includesavolume control rectifier having its control grid connected to thecontrolfgridbf an amplier to be con- Still other objects of the presentinvention are ,to improve generally the simplicity and efficiency vofautomatic gain control networksv ofradio receivers, and particularly toprovide such a network which is not only reliable in operation, buteconomically manufactured and assembled in a radio receiver. l

- `The novel features which I believe to be characteristic of myinventionare set forth in particularity in the appended claims, theinvention itself, however, as to both its organization and (Cl. Z50-20)i method of roperation will best be understood by reference to thefollowing description taken in connection with the drawing in which Ihave indicated Vdiagrammatically several circuit'forganizations wherebymy invention may be carried into effect.

In the drawing, A

Fig. 1 diagrammatically shows a receiving circuit embodying one form ofthe invention,

Fig. 2 shows a modied application of the invention. i

Referring now to the accompanying drawing, wherein like referencecharacters in the different figures represent similar circuit elements,there'is shown in Fig. l a radio receiver,'of the superheterodyne type,which embodies an automatic gain control network. In general, theautomatic gain control arrangement'shown in Fig. 1 follows thearrangement disclosed and claimed by K. A. Chittick and W. L. Carlson inapplication Serial pose of simplification of descriptionhowever, theaforementioned arrangementfin the said co-pending application has beensimplified. The source of signals l may comprise the usual groundedantenna circuit, and the sourceis shown coupled,

as at M, to the inputelectrodes of a radio frequency amplifier tube 2,the latter being of the screen grid type, and including an indirectlyheated cathode. The variable tuning condenser 3 is connected across the'coil 4, Vand the rotor No. 642,544, med November 14, 1932. For thepurdesignates the well lknown uni-control tuning ,means While a combineddetector-oscillator circuitis shown in Fig. 1, it is to be clearlyunderstood that separate tubes may be employed in distinct localloscillator and first detector stages,

in a manner well known to those skilled in the art. Since the detailsofthe detector oscillator circuit are not necessary to a properunderstanding of the present invention, this circuit'is conventionallyshown.

The intermediate frequency output of the de- `tectoroscillator isimpressed across the input electrodes of the intermediate frequencyamplifier tube 2', ,the latter being of the same type as the tube 2. Thecoupling network Mz between the work M3 between the tube 2 andthersecond detector is of the same type as the coupling Y.network M2.

The automatic Volume control network comprises a screen grid tube 9;ro`f'the indirectly heatled cathode type, the control grid of the tube 9being connected to the control grid of tube =2 through a path whichcomprises thelead IU. In

order to furnish proper negative'bias for the ycontrol grid of tube-9,the cathode `of the tube isv connectedbyleadl] to point don resistor P.'

The anode of'. tube '9 is connected to the source ofpositiye potential B(this source not being shown) through aresistor I2 having a highref'sistive magnitude.v The anode 'side of the resistor I2 is connected toground through a .series path including thevoltage regulator'elen'ientVI3 Yand the resistorl I4. The resistor P is connected in parallel withthelast named seriesv path I 3, I4.

The resistor "I4 has a low resistive magnitude, and the voltage.regulator element I3 can be said to haveafalling resistancecharacteristic since i R decreases as I increases. To secure automaticgain control of the radio frequency 4ampliiier and intermediatefrequency amplier, the high potential side of resistor 'I 4 is connected`through a lead I5 Ato the controlgri'd vcircuits of tubes"2 and 2. `Thecontrol grid of tube'2 is connected to the lead The resistor yIl Yhas-ahigh resistance and is connected to groundrrfrom lead I5. .The lead I'Bis Aconnected to a .point e on resistor "Il such that kthe ,c biascontrol .actionon the control grids of tubes 2 and 'Z'.Ais graded. Thatisthe controlstarts on all.y tubes a't `thesame time, 'but the amount offcontrol isgraded sothat oneitubegets more than ftheiotl'ier.` vIi'iforder to adjust the level at which automaticjvolume control actionis to commence,

`an 'adjustablev slider jij!!A is provided.

` The voltage `regulator element 'I3 consists 4substantially of aYcarborundum disc. lThe Vopposite faces of, thedisc are provided `Withmetallic -elec-- l' `tionsfrom theanode of tube '9 and theungroundtrodes I3', and these electrodesare usually pro- 4 vided ontheoppos'ite faces ofthe disc v'by spraying discs o'f metal. on thesefaces. The connecedside'o'f there'sistor I4 are 'made to thesevmetallicd'iscsfl" 'I'hepropertyof the voltageregulatorA element` is tomaintain th'evoltage drop .across it, when currentjows tlfierethrough,sub- L fstantially constant.' Reference isjmade to page 93 .ofan.article entitled 'llhyrite vappearing in Ythe General .Electric Reviewl,for February, 1930,

for 'a description .-.offthe electrical .characteristics --of kthevoltage regulator element I'Li.

."-Ihe operation of athe invention Willnow be 'clearly understoodin Viewof the afore'going description.. jThe `'automatic'volume control:network functions'in theusual manner, the potential drop`Aacrossthe.control.,grid bias '.resistor: I4 varying 'l With-.theintensity-of 4the signal energy impressed Y upon the vcon-trol .grid oftube 9. An increase in 'signal energy-impressed on .the control Vgrid oftube .9 results in `thepoint on .resistor I4 to Which the slider I9 isconnecte'dbecoming less positive with respect to ground, or negative endof plate supply Voltage. This results in the control grids of tubes 2and 2 becoming more negative With respect to their associated cathodes,the latter being positive With respect to ground. Thus, the gain of thestages including tubes 2 and 2 is reduced. With decreasing signalvoltage, the reverse action'takes place.

If the voltage regulator element I3 were not used in series with thecontrol bias resistor I 4, but

la resistor substituted for this Voltage regulator element, there wouldbe secured a lesser percentage drop across the resistor I4 for a givensignal current increase. In other Words, in View of the factt-hat'the'voltage drop across the element I3 is substantially constantover a Wide range of current variation, there is secured a largerpercentage drop across the control bias resistor I4 for a given signalcurrent increase, than if the element I3 were omitted and replaced by aresistor. Hence, the stiffness of the automatic volume control actionhas been substantially increased, and in an economicalmanner since thecost of the element YI3 is negligible -compared to that of the,customary circuit elements utilized.

In Fig. '2 fis shown a modiflcationof the invention wherein the screengrid potentials of the radio frequency amplifier tube 2 and theintermediate V`frequency amplifier tube 2' are auto- Atube 9. The volumecontrolrectier 9 has its anode, in this case, connected `bythe leadV I5' to the screen grid Velectrodes Vof tubes 2 and "2.

In this application .of the invention AWhenthe v( intensitylof thesignal'energy appliedto the control grid 'of tube'9 increases,l thecontrolpotential applied `to the screen ,.gridsxJof tubes 2 and 2'through lead I5. decreases. c l Y `A neon tube couldbe usedin place ofelement .I.3. When such a neon .lamp is placed in series.

cated and-described several systems for' carrying .my vinvention intoeffect it willbeapparent to vone l .skilled the art that myinventionilsr by 'no .means limited to the 'particular organizationsshown and described, but'that many modifications rmay be made Withoutdeparting from the scope of my invention as set forth in the appendedclaims.

WhatIclaimis: y 1. In an automatic'. gain control arrangement for aradio receiver, an amplifier to b e 'controlled .as to gain, a rectifierconnected to the input cir--- cuit of the amplifer,. a path in the'outputfcircuit of the rectifier including a bias control resistor, adirect currentY connection from said resistor to `an input electrode ofsaidamplifier, said path including'an .additional element composed ofsilicon carbide and Vhaving an electrical characteristic such that thebias control variation voltage takes place across 'saidresiston 2. In anautomatic gain control arrangement for a radio receiver, .an amplier tobe controlledas .to gain, a rectifier connected to the amplifier, a pathin the output circuit ofthe rectier including a bias control resistor, adirect current connection from'said resistor to a gain control electrodeof 'said amplifier, said path including lan additional elementvconsisting substantially of carborundum and having an electrical charac-.teristic such that the bias control variation lvoltage takes Yplaceacross said resistor. i'

3. In an automatic gain control arrangement Cil for a radio receiver, anamplifier to be controlled as to gain, a rectifier connected to theampliier, a path in the output circuit of the rectier including a biascontrol resistor, a direct current connection from said resistor to acold gain control electrode of said amplier, said path including anadditional element composed substantially of silicon carbide and havingan electrical characteristic such that the resistance of the elementdecreases as the current iiow therethrough increases whereby the biascontrol variation voltage takes place across said resistor.

4. In an automatic gain control arrangement for a radio receiver, anamplifier to be controlled as to gain, a rectifier connected to theamplier, a path in the output circuit of theV rectifier including a biascontrol resistor, a direct current connection from said resistor to apositive cold electrode of said amplifier, said path including anadditional element composed of carborundum having an electricalcharacteristic such that the bias control variation voltage takes placeacross said resistor.

5. In a signaling system of the type including a signal transmissiontube, an electron discharge tube having a signal input circuit and animpedance in its space current path, and a direct current connectionbetween a point on said imped-v ance and an electrode of saidtransmission tube whereby the transmission of signals through the iirsttube is a function of a gain control voltage developed across theimpedance, and a device in the space current path of said second tubehaving a resistance characteristic such that the voltage developedthereacross by the space current fiow is substantially constant over awide range of current variation whereby said gain control voltage isdeveloped substantially across the said impedance.

6. In a system as defined in claim 5, said device being arranged inseries with said impedance, and said electrode being the signal controlgrid.

7. In a signaling system of the type including a signal transmissiontube, an electron discharge tube having a signal input circuit and animpedance in its space current path, and a direct current connectionbetween a point on said impedance and an electrode of said transmissiontube whereby the transmission of signals through the iirst tube is afunction of the voltage developed across the impedance, a device in thespace current path of said second tube having a resistancecharacteristic such that the voltage developed thereacross by the spacecurrent flow is substantially constant over a wide range of currentvariation, said device consisting of an element composed substantiallyof silicon carbide.

RENE A. BRADEN.

